FIELD TRIP TO NIMET ENUGU- AGIDI

                   

HISTORY:

In Nigeria, metrological services started in 1892when the first weather observatory was established by the British colonial government at the Race course, Lagos. Thereafter the Metrological Department operated under various ministries at different times until June 2003 when the Nigerian Metrological agency bill was passed and signed into law thereby creating NIMET as a parastatal under the Federal Ministry of Aviation.

   One of the functions of NIMET is to promote the services of metrological agency in agricultural, drought and desertification activities.

INTRODUCTION:

Metrology is the scientific study of atmospheric phenomena as related to weather. Metrology is based on physics and mathematics.

The word 'metrology' was coined from a book, 'Metrologica' which was written by Aristotle, the Greek scientist and philosopher around 340 BC.

Climatology is basically an empirical science that is firmly rooted in weather observation and measurement. Climatology is the scientific study of climate which is the synthesis of weather over a long period conventionally taken as 30 years. Climate therefore represents the characteristic conditions of the atmosphere over an area or location deduced from repeated weather observation and measurement over a period of time.

                                        

                                       

                                   WEATHER INSTRUMENT

First of all, we talk about the metrological enclosure. It should be a level ground. No tall instrument around the enclosure to avoid them casting shadows on the instruments.

Dimension: standard measurement =20m ×20m

FIG A: LAYOUT OF A WEATHER STATION

Weather observation and measurement can take place from various platforms on the earth's surface, in the atmosphere and in space.

various weather instruments are used to measure weather elements. Some are active sensors that are directly immersed within the atmosphere. Others are remote sensors which measure weather elements from a distance without direct physical contact with the parameters being measured. Weather instruments may also be categorised into two types depending on whether they are self recording (autographic) or non-self recording ( manual). The former instruments provide continuous measurement of weather elements over a defined period of time. The latter instruments have to be read by observers at chosen times of the day.

* AUTOMATIC WEATHER SYSTEM

Has the ability of giving all the records that is taken manually. It has a sensor that will send the reading to the office. from the computers, you can get all the readings automatically.

FIG. B:AWS ( Automatic Weather System)

The measurings that can be gotten from this include;

§  Temperature

§  Dry bulb reading

§  Wet bulb reading

§  Rainfall value

§  thunderstorm

§  Radiation

§  Wind speed and direction

* WIND VANE

Wind vane has a tail and a head, the head is a pointer that shows the direction the wind is blowing from. Win direction is observed with the aid of a windvane. The device consists of a horizontal arm pivoted on a steel spindle with a pointer at one end. 

* CUP-COUNTER ANEMOMETER

Wind speed is measured with the aid of cup anemometer which consists of three or four cups conical or hemispherical in shape, mounted symmetrically about a vertical axis. The cups rotate according to the prevailing wind speed. Measures wind speed in KM.

FIG. C: CUP-COUNTER ANEMOMETER

* RAINGUAGE

Rainfall is measured by the use of a rain gauge. The rain gauge collects rainfall over a funnel of a known area (limited by its rim). The amount of rain water collected is poured into a graduated measuring jar where it is indicated in units of depth such as millimetres. The rain gauge provides the total volume of rain that falls between two observation times. The rain gauge is conventionally read at 0900 hours and the amount of rain measured is credited to the preceeding 24 hour period.

  Several factors determine the amount of rain that a given rain gauge is able to catch. These include the siting and exposure of the rain gauge and wind speed. Wind produces turbulent eddies around and over the rain gauge. Rain gauge must therefore be carefully sited to avoid interference of nearby objects with the amount of rain caught. No tree,  building or any other object should be near the rain gauge to minimize the effect of a possible interference.                                                              

                       

FIG. D: MANUAL RAIN GAUGE

We were told about the tilting siphon autographic rain gauge that contains a collecting chamber fitted with a float. As the rain falls and the chamber fills up, the float rises and a pen attached to the traces a graph on a chart fixed to a cylindrical drum driven by clock work. When the chamber is filled up, it tilts over on its pivot and the content siphon out of the gauge. The float returns to its original level and the now rests at the base of the chart. One complete cycle measures 5mm of rainfall. On the autographic rain chart, the horizontal lines represent the amount of rainfall in millimetres while the vertical lines represent rainfall duration in hours and minutes.

FIG. E: AUTOMATIC  RAIN GUAGE

* SOIL THERMOMETER

Soil thermometers are used for measuring soil temperatures at various depths. These are usually mercurial thermometers with the bulbs embedded in paraffin wax. The thermometers are suspended in steel tubes and inserted into the soil at various depths. The depths at which soil temperatures are measured are 5cm, 10cm, 20cm, 50cm and 100cm. For shallower depths, mercurial thermometers with their stems bent at right angles for reading convenience are used. The 5cm thermometer measures temperature of the soil at 5cm depth, it is closer to the surface therefore it is the most sensitive because it captures almost what happens at the surface (temperature of the top soil)

FIG. F:SOIL THERMOMETER

*  CAMPBELL-STOKES SUNSHINE RECORDER

The duration of sunshine is measured with the aid of Campbell-Stokes sunshine recorder. It consists of a glass sphere which focuses the rays of the sun on a sensitised card graduated in hours and minutes and held in a metal half-bowl with which the sphere is concentric. The instrument is mounted in the open on a concrete pillar about 1.5m above the ground. Bright sunshine traces a burnt line along the sensitised card while cloudy periods are blank. The total duration of sunshine for the day is obtained by measuring the total length of the burnt traces on the card which is rendered in hours and minutes.

FIG. G:CAMPBELL STOKES RECORDER

*  EVAPORIMETER

Evaporation is measured by the use of what are generally called evaporimeters.

Evaporation is the conversion of moisture into vapour form and its removal and transport upwards into the atmosphere. The process of water loss from a vegetated surface is referred to as evapotranspiration.

Piche evaporimeter is used to measure the rate of evaporation (in mililitres). it is a graduated measuring cylindrical tube enclosed at one end and containing water. A disk of filter paper is attached to the open end and the paper is kept continuously moist by a wick linking it to a small water container. The instrument is kept within the Stevenson's screen. The Piche evaporimeter is not very reliable and it has been criticised as measuring the drying power of the air rather than the amount of water lost by evaporation to the atmosphere. Hence, evaporation pans are more commonly used at weather stations. There are different types of evaporation pans depending on their size, shape and manner of exposure.

Class A pan which has been recommended for world-wide use by the WMO (World Metrological Organization), is a cylindrical pan with a diameter of 1206mm and 2.54mm deep. It is used to measure amount of evaporation. It is filled with water to within 51mm of the rim and mounted on a wooden platform so that the water surface within the pan is 305mm above the ground. It is painted aluminium white. The pan is filled with water to the appropriate level and left in the open away from any obstacles, in the weather station. After a period of time which is usually 24 hours, the level of water in the pan is checked. Unless some rain has fallen during the intervening period, the level of water in the pan would have fallen owing to evaporation. The pan is reset by filling it back with water to the original level. The amount of water added to reset the pan represents the evaporation that has occurred in the intervening period.

       FIG. H: CLASS A PAN

 *  MINIMUM AND MAXIMUM THERMOMETERS

 Air temperature is measured manually with the aid of maximum and minimum thermometers. They are housed in a Stevenson's screen, this is a wooden louvred cupboard with a hinged door mounted on a steel. It is painted white. The louvred sides allow adequate ventilation while the white paint prevents absorption of solar radiation by the shelter. The thermometers placed within the Stevenson screen thus give a close approximation to the true air temperature undisturbed by the effects of direct solar or terrestrial radiaton.

        

           FIG. I: STEVENSON SCREEN

 The maximum thermometer is a mercury-in- glass thermometer containing a small glass index which the mercury pushes along when air temperature rises but leaves behind when the temperature falls.

The minimum thermometer is an alcohol-in-glass thermometer in which when the temperature rises the alcohol expands and flows past the index and when the temperature falls the alcohol contracts and drags the index back because of its surface tension. The end of the index nearer the meniscus shows the minimum temperature and the instrument is reset by tilting. The maximum and minimum thermometers are used at weather stations to measure the highest and lowest temperatures within the day respectively.

FIG. J: MINIMUM AND MAXIMUM THERMOMETERS

*  WET AND DRY BULB THERMOMETER

 The relative humidity of the air is measured manually at a weather station with the aid of wet and dry  bulb thermometers. It is housed in the Stevenson screen. The dry bulb thermometer has its bulb covered with muslin perpetually wetted with pure water. This gives the wet bulb reading which in unsaturated air is less than the dry bulb temperature. This is because the latent heat required to evaporate water from the muslin is supplied by air in contact with the wet bulb.   

When relative humidity= 100% , amount of water going up is equal to that coming down.

FIG. K: WET AND DRY THERMOMETER

*  GRASS MINIMUM THERMOMETER

A type of minimum thermometer used to measure the lowest temperature above uniform short grasses. It is used to measure ground temperature.

* CLOUD

If the whole sky is covered by cloud, it is called overcast i.e we have 8 octas covering the sky.

Classification:

High clouds- Cirrus, cirro-stratos, cirro-cumulus

Medium clouds- Alto-cumulus, Nimbostratus, Alto-stratos

Low clouds- Cumulus, stratos, strato-cumulus, Cummulo nimbos

Alto-cumulus is in form of ridges.

Cumulus is in form of cotton wool, white in colour.

When alto-stratos is seen it means that rainfall is at hand.

Stratos moves fast.

*  VISIBILITY

Visibility means seeing and recognizing.

Ø Less than 6km means poor visibility

Ø 10km and above means very good visibility

Ø 6km-9km means fair visibility.

RELEVANCE OF THE VISIT TO NIMET TO CROP SCIENCE

Weather and climate have always been part of the physical environment in which the human society thrives. The weather and climate characteristics of any place on earth determine the types of crops that are grown for food. It is  said that of all the human activities, agriculture which provides food for people and contributes significantly to the economies of nations, is the most sensitive to weather. Normal weather conditions are associated with good crop yield and positive economic impact.

soil thermometer is of immerse importance to agriculture. Because there are some crops that are shallow rooted and others that are deep-rooted. It helps to know at what depth to plant the particular crop so as to have its maximum yield.

The thermometer gives various conditions at various depths which help to determine the temperature at which different crops can thrive.

Some crops need some kind of heat to thrive while some need cold conditions.

                      FIELD TRIP TO NIMET ENUGU- AGIDI

HISTORY:

In Nigeria, metrological services started in 1892when the first weather observatory was established by the British colonial government at the Race course, Lagos. Thereafter the Metrological Department operated under various ministries at different times until June 2003 when the Nigerian Metrological agency bill was passed and signed into law thereby creating NIMET as a parastatal under the Federal Ministry of Aviation.

   One of the functions of NIMET is to promote the services of metrological agency in agricultural, drought and desertification activities.

INTRODUCTION:

Metrology is the scientific study of atmospheric phenomena as related to weather. Metrology is based on physics and mathematics.

The word 'metrology' was coined from a book, 'Metrologica' which was written by Aristotle, the Greek scientist and philosopher around 340 BC.

Climatology is basically an empirical science that is firmly rooted in weather observation and measurement. Climatology is the scientific study of climate which is the synthesis of weather over a long period conventionally taken as 30 years. Climate therefore represents the characteristic conditions of the atmosphere over an area or location deduced from repeated weather observation and measurement over a period of time.

                                        

                                       

                                   WEATHER INSTRUMENT

First of all, we talk about the metrological enclosure. It should be a level ground. No tall instrument around the enclosure to avoid them casting shadows on the instruments.

Dimension: standard measurement =20m ×20m

FIG A: LAYOUT OF A WEATHER STATION

Weather observation and measurement can take place from various platforms on the earth's surface, in the atmosphere and in space.

various weather instruments are used to measure weather elements. Some are active sensors that are directly immersed within the atmosphere. Others are remote sensors which measure weather elements from a distance without direct physical contact with the parameters being measured. Weather instruments may also be categorised into two types depending on whether they are self recording (autographic) or non-self recording ( manual). The former instruments provide continuous measurement of weather elements over a defined period of time. The latter instruments have to be read by observers at chosen times of the day.

* AUTOMATIC WEATHER SYSTEM

Has the ability of giving all the records that is taken manually. It has a sensor that will send the reading to the office. from the computers, you can get all the readings automatically.

FIG. B:AWS ( Automatic Weather System)

The measurings that can be gotten from this include;

§  Temperature

§  Dry bulb reading

§  Wet bulb reading

§  Rainfall value

§  thunderstorm

§  Radiation

§  Wind speed and direction

* WIND VANE

Wind vane has a tail and a head, the head is a pointer that shows the direction the wind is blowing from. Win direction is observed with the aid of a windvane. The device consists of a horizontal arm pivoted on a steel spindle with a pointer at one end. 

* CUP-COUNTER ANEMOMETER

Wind speed is measured with the aid of cup anemometer which consists of three or four cups conical or hemispherical in shape, mounted symmetrically about a vertical axis. The cups rotate according to the prevailing wind speed. Measures wind speed in KM.

FIG. C: CUP-COUNTER ANEMOMETER

* RAINGUAGE

Rainfall is measured by the use of a rain gauge. The rain gauge collects rainfall over a funnel of a known area (limited by its rim). The amount of rain water collected is poured into a graduated measuring jar where it is indicated in units of depth such as millimetres. The rain gauge provides the total volume of rain that falls between two observation times. The rain gauge is conventionally read at 0900 hours and the amount of rain measured is credited to the preceeding 24 hour period.

  Several factors determine the amount of rain that a given rain gauge is able to catch. These include the siting and exposure of the rain gauge and wind speed. Wind produces turbulent eddies around and over the rain gauge. Rain gauge must therefore be carefully sited to avoid interference of nearby objects with the amount of rain caught. No tree,  building or any other object should be near the rain gauge to minimize the effect of a possible interference.                                                              

                       

FIG. D: MANUAL RAIN GAUGE

We were told about the tilting siphon autographic rain gauge that contains a collecting chamber fitted with a float. As the rain falls and the chamber fills up, the float rises and a pen attached to the traces a graph on a chart fixed to a cylindrical drum driven by clock work. When the chamber is filled up, it tilts over on its pivot and the content siphon out of the gauge. The float returns to its original level and the now rests at the base of the chart. One complete cycle measures 5mm of rainfall. On the autographic rain chart, the horizontal lines represent the amount of rainfall in millimetres while the vertical lines represent rainfall duration in hours and minutes.

FIG. E: AUTOMATIC  RAIN GUAGE

* SOIL THERMOMETER

Soil thermometers are used for measuring soil temperatures at various depths. These are usually mercurial thermometers with the bulbs embedded in paraffin wax. The thermometers are suspended in steel tubes and inserted into the soil at various depths. The depths at which soil temperatures are measured are 5cm, 10cm, 20cm, 50cm and 100cm. For shallower depths, mercurial thermometers with their stems bent at right angles for reading convenience are used. The 5cm thermometer measures temperature of the soil at 5cm depth, it is closer to the surface therefore it is the most sensitive because it captures almost what happens at the surface (temperature of the top soil)

FIG. F:SOIL THERMOMETER

*  CAMPBELL-STOKES SUNSHINE RECORDER

The duration of sunshine is measured with the aid of Campbell-Stokes sunshine recorder. It consists of a glass sphere which focuses the rays of the sun on a sensitised card graduated in hours and minutes and held in a metal half-bowl with which the sphere is concentric. The instrument is mounted in the open on a concrete pillar about 1.5m above the ground. Bright sunshine traces a burnt line along the sensitised card while cloudy periods are blank. The total duration of sunshine for the day is obtained by measuring the total length of the burnt traces on the card which is rendered in hours and minutes.

FIG. G:CAMPBELL STOKES RECORDER

*  EVAPORIMETER

Evaporation is measured by the use of what are generally called evaporimeters.

Evaporation is the conversion of moisture into vapour form and its removal and transport upwards into the atmosphere. The process of water loss from a vegetated surface is referred to as evapotranspiration.

Piche evaporimeter is used to measure the rate of evaporation (in mililitres). it is a graduated measuring cylindrical tube enclosed at one end and containing water. A disk of filter paper is attached to the open end and the paper is kept continuously moist by a wick linking it to a small water container. The instrument is kept within the Stevenson's screen. The Piche evaporimeter is not very reliable and it has been criticised as measuring the drying power of the air rather than the amount of water lost by evaporation to the atmosphere. Hence, evaporation pans are more commonly used at weather stations. There are different types of evaporation pans depending on their size, shape and manner of exposure.

Class A pan which has been recommended for world-wide use by the WMO (World Metrological Organization), is a cylindrical pan with a diameter of 1206mm and 2.54mm deep. It is used to measure amount of evaporation. It is filled with water to within 51mm of the rim and mounted on a wooden platform so that the water surface within the pan is 305mm above the ground. It is painted aluminium white. The pan is filled with water to the appropriate level and left in the open away from any obstacles, in the weather station. After a period of time which is usually 24 hours, the level of water in the pan is checked. Unless some rain has fallen during the intervening period, the level of water in the pan would have fallen owing to evaporation. The pan is reset by filling it back with water to the original level. The amount of water added to reset the pan represents the evaporation that has occurred in the intervening period.

       FIG. H: CLASS A PAN

 *  MINIMUM AND MAXIMUM THERMOMETERS

 Air temperature is measured manually with the aid of maximum and minimum thermometers. They are housed in a Stevenson's screen, this is a wooden louvred cupboard with a hinged door mounted on a steel. It is painted white. The louvred sides allow adequate ventilation while the white paint prevents absorption of solar radiation by the shelter. The thermometers placed within the Stevenson screen thus give a close approximation to the true air temperature undisturbed by the effects of direct solar or terrestrial radiaton.

        

           FIG. I: STEVENSON SCREEN

 The maximum thermometer is a mercury-in- glass thermometer containing a small glass index which the mercury pushes along when air temperature rises but leaves behind when the temperature falls.

The minimum thermometer is an alcohol-in-glass thermometer in which when the temperature rises the alcohol expands and flows past the index and when the temperature falls the alcohol contracts and drags the index back because of its surface tension. The end of the index nearer the meniscus shows the minimum temperature and the instrument is reset by tilting. The maximum and minimum thermometers are used at weather stations to measure the highest and lowest temperatures within the day respectively.

FIG. J: MINIMUM AND MAXIMUM THERMOMETERS

*  WET AND DRY BULB THERMOMETER

 The relative humidity of the air is measured manually at a weather station with the aid of wet and dry  bulb thermometers. It is housed in the Stevenson screen. The dry bulb thermometer has its bulb covered with muslin perpetually wetted with pure water. This gives the wet bulb reading which in unsaturated air is less than the dry bulb temperature. This is because the latent heat required to evaporate water from the muslin is supplied by air in contact with the wet bulb.   

When relative humidity= 100% , amount of water going up is equal to that coming down.

FIG. K: WET AND DRY THERMOMETER

*  GRASS MINIMUM THERMOMETER

A type of minimum thermometer used to measure the lowest temperature above uniform short grasses. It is used to measure ground temperature.

* CLOUD

If the whole sky is covered by cloud, it is called overcast i.e we have 8 octas covering the sky.

Classification:

High clouds- Cirrus, cirro-stratos, cirro-cumulus

Medium clouds- Alto-cumulus, Nimbostratus, Alto-stratos

Low clouds- Cumulus, stratos, strato-cumulus, Cummulo nimbos

Alto-cumulus is in form of ridges.

Cumulus is in form of cotton wool, white in colour.

When alto-stratos is seen it means that rainfall is at hand.

Stratos moves fast.

*  VISIBILITY

Visibility means seeing and recognizing.

Ø Less than 6km means poor visibility

Ø 10km and above means very good visibility

Ø 6km-9km means fair visibility.

RELEVANCE OF THE VISIT TO NIMET TO CROP SCIENCE

Weather and climate have always been part of the physical environment in which the human society thrives. The weather and climate characteristics of any place on earth determine the types of crops that are grown for food. It is  said that of all the human activities, agriculture which provides food for people and contributes significantly to the economies of nations, is the most sensitive to weather. Normal weather conditions are associated with good crop yield and positive economic impact.

soil thermometer is of immerse importance to agriculture. Because there are some crops that are shallow rooted and others that are deep-rooted. It helps to know at what depth to plant the particular crop so as to have its maximum yield.

The thermometer gives various conditions at various depths which help to determine the temperature at which different crops can thrive.

Some crops need some kind of heat to thrive while some need cold conditions.

                      FIELD TRIP TO NIMET ENUGU- AGIDI

HISTORY:

In Nigeria, metrological services started in 1892when the first weather observatory was established by the British colonial government at the Race course, Lagos. Thereafter the Metrological Department operated under various ministries at different times until June 2003 when the Nigerian Metrological agency bill was passed and signed into law thereby creating NIMET as a parastatal under the Federal Ministry of Aviation.

   One of the functions of NIMET is to promote the services of metrological agency in agricultural, drought and desertification activities.

INTRODUCTION:

Metrology is the scientific study of atmospheric phenomena as related to weather. Metrology is based on physics and mathematics.

The word 'metrology' was coined from a book, 'Metrologica' which was written by Aristotle, the Greek scientist and philosopher around 340 BC.

Climatology is basically an empirical science that is firmly rooted in weather observation and measurement. Climatology is the scientific study of climate which is the synthesis of weather over a long period conventionally taken as 30 years. Climate therefore represents the characteristic conditions of the atmosphere over an area or location deduced from repeated weather observation and measurement over a period of time.

                                        

                                       

                                   WEATHER INSTRUMENT

First of all, we talk about the metrological enclosure. It should be a level ground. No tall instrument around the enclosure to avoid them casting shadows on the instruments.

Dimension: standard measurement =20m ×20m

FIG A: LAYOUT OF A WEATHER STATION

Weather observation and measurement can take place from various platforms on the earth's surface, in the atmosphere and in space.

various weather instruments are used to measure weather elements. Some are active sensors that are directly immersed within the atmosphere. Others are remote sensors which measure weather elements from a distance without direct physical contact with the parameters being measured. Weather instruments may also be categorised into two types depending on whether they are self recording (autographic) or non-self recording ( manual). The former instruments provide continuous measurement of weather elements over a defined period of time. The latter instruments have to be read by observers at chosen times of the day.

* AUTOMATIC WEATHER SYSTEM

Has the ability of giving all the records that is taken manually. It has a sensor that will send the reading to the office. from the computers, you can get all the readings automatically.

FIG. B:AWS ( Automatic Weather System)

The measurings that can be gotten from this include;

§  Temperature

§  Dry bulb reading

§  Wet bulb reading

§  Rainfall value

§  thunderstorm

§  Radiation

§  Wind speed and direction

* WIND VANE

Wind vane has a tail and a head, the head is a pointer that shows the direction the wind is blowing from. Win direction is observed with the aid of a windvane. The device consists of a horizontal arm pivoted on a steel spindle with a pointer at one end. 

* CUP-COUNTER ANEMOMETER

Wind speed is measured with the aid of cup anemometer which consists of three or four cups conical or hemispherical in shape, mounted symmetrically about a vertical axis. The cups rotate according to the prevailing wind speed. Measures wind speed in KM.

FIG. C: CUP-COUNTER ANEMOMETER

* RAINGUAGE

Rainfall is measured by the use of a rain gauge. The rain gauge collects rainfall over a funnel of a known area (limited by its rim). The amount of rain water collected is poured into a graduated measuring jar where it is indicated in units of depth such as millimetres. The rain gauge provides the total volume of rain that falls between two observation times. The rain gauge is conventionally read at 0900 hours and the amount of rain measured is credited to the preceeding 24 hour period.

  Several factors determine the amount of rain that a given rain gauge is able to catch. These include the siting and exposure of the rain gauge and wind speed. Wind produces turbulent eddies around and over the rain gauge. Rain gauge must therefore be carefully sited to avoid interference of nearby objects with the amount of rain caught. No tree,  building or any other object should be near the rain gauge to minimize the effect of a possible interference.                                                              

                       

FIG. D: MANUAL RAIN GAUGE

We were told about the tilting siphon autographic rain gauge that contains a collecting chamber fitted with a float. As the rain falls and the chamber fills up, the float rises and a pen attached to the traces a graph on a chart fixed to a cylindrical drum driven by clock work. When the chamber is filled up, it tilts over on its pivot and the content siphon out of the gauge. The float returns to its original level and the now rests at the base of the chart. One complete cycle measures 5mm of rainfall. On the autographic rain chart, the horizontal lines represent the amount of rainfall in millimetres while the vertical lines represent rainfall duration in hours and minutes.

FIG. E: AUTOMATIC  RAIN GUAGE

* SOIL THERMOMETER

Soil thermometers are used for measuring soil temperatures at various depths. These are usually mercurial thermometers with the bulbs embedded in paraffin wax. The thermometers are suspended in steel tubes and inserted into the soil at various depths. The depths at which soil temperatures are measured are 5cm, 10cm, 20cm, 50cm and 100cm. For shallower depths, mercurial thermometers with their stems bent at right angles for reading convenience are used. The 5cm thermometer measures temperature of the soil at 5cm depth, it is closer to the surface therefore it is the most sensitive because it captures almost what happens at the surface (temperature of the top soil)

FIG. F:SOIL THERMOMETER

*  CAMPBELL-STOKES SUNSHINE RECORDER

The duration of sunshine is measured with the aid of Campbell-Stokes sunshine recorder. It consists of a glass sphere which focuses the rays of the sun on a sensitised card graduated in hours and minutes and held in a metal half-bowl with which the sphere is concentric. The instrument is mounted in the open on a concrete pillar about 1.5m above the ground. Bright sunshine traces a burnt line along the sensitised card while cloudy periods are blank. The total duration of sunshine for the day is obtained by measuring the total length of the burnt traces on the card which is rendered in hours and minutes.

FIG. G:CAMPBELL STOKES RECORDER

*  EVAPORIMETER

Evaporation is measured by the use of what are generally called evaporimeters.

Evaporation is the conversion of moisture into vapour form and its removal and transport upwards into the atmosphere. The process of water loss from a vegetated surface is referred to as evapotranspiration.

Piche evaporimeter is used to measure the rate of evaporation (in mililitres). it is a graduated measuring cylindrical tube enclosed at one end and containing water. A disk of filter paper is attached to the open end and the paper is kept continuously moist by a wick linking it to a small water container. The instrument is kept within the Stevenson's screen. The Piche evaporimeter is not very reliable and it has been criticised as measuring the drying power of the air rather than the amount of water lost by evaporation to the atmosphere. Hence, evaporation pans are more commonly used at weather stations. There are different types of evaporation pans depending on their size, shape and manner of exposure.

Class A pan which has been recommended for world-wide use by the WMO (World Metrological Organization), is a cylindrical pan with a diameter of 1206mm and 2.54mm deep. It is used to measure amount of evaporation. It is filled with water to within 51mm of the rim and mounted on a wooden platform so that the water surface within the pan is 305mm above the ground. It is painted aluminium white. The pan is filled with water to the appropriate level and left in the open away from any obstacles, in the weather station. After a period of time which is usually 24 hours, the level of water in the pan is checked. Unless some rain has fallen during the intervening period, the level of water in the pan would have fallen owing to evaporation. The pan is reset by filling it back with water to the original level. The amount of water added to reset the pan represents the evaporation that has occurred in the intervening period.

       FIG. H: CLASS A PAN

 *  MINIMUM AND MAXIMUM THERMOMETERS

 Air temperature is measured manually with the aid of maximum and minimum thermometers. They are housed in a Stevenson's screen, this is a wooden louvred cupboard with a hinged door mounted on a steel. It is painted white. The louvred sides allow adequate ventilation while the white paint prevents absorption of solar radiation by the shelter. The thermometers placed within the Stevenson screen thus give a close approximation to the true air temperature undisturbed by the effects of direct solar or terrestrial radiaton.

        

           FIG. I: STEVENSON SCREEN

 The maximum thermometer is a mercury-in- glass thermometer containing a small glass index which the mercury pushes along when air temperature rises but leaves behind when the temperature falls.

The minimum thermometer is an alcohol-in-glass thermometer in which when the temperature rises the alcohol expands and flows past the index and when the temperature falls the alcohol contracts and drags the index back because of its surface tension. The end of the index nearer the meniscus shows the minimum temperature and the instrument is reset by tilting. The maximum and minimum thermometers are used at weather stations to measure the highest and lowest temperatures within the day respectively.

FIG. J: MINIMUM AND MAXIMUM THERMOMETERS

*  WET AND DRY BULB THERMOMETER

 The relative humidity of the air is measured manually at a weather station with the aid of wet and dry  bulb thermometers. It is housed in the Stevenson screen. The dry bulb thermometer has its bulb covered with muslin perpetually wetted with pure water. This gives the wet bulb reading which in unsaturated air is less than the dry bulb temperature. This is because the latent heat required to evaporate water from the muslin is supplied by air in contact with the wet bulb.   

When relative humidity= 100% , amount of water going up is equal to that coming down.

FIG. K: WET AND DRY THERMOMETER

*  GRASS MINIMUM THERMOMETER

A type of minimum thermometer used to measure the lowest temperature above uniform short grasses. It is used to measure ground temperature.

* CLOUD

If the whole sky is covered by cloud, it is called overcast i.e we have 8 octas covering the sky.

Classification:

High clouds- Cirrus, cirro-stratos, cirro-cumulus

Medium clouds- Alto-cumulus, Nimbostratus, Alto-stratos

Low clouds- Cumulus, stratos, strato-cumulus, Cummulo nimbos

Alto-cumulus is in form of ridges.

Cumulus is in form of cotton wool, white in colour.

When alto-stratos is seen it means that rainfall is at hand.

Stratos moves fast.

*  VISIBILITY

Visibility means seeing and recognizing.

Ø Less than 6km means poor visibility

Ø 10km and above means very good visibility

Ø 6km-9km means fair visibility.

RELEVANCE OF THE VISIT TO NIMET TO CROP SCIENCE

Weather and climate have always been part of the physical environment in which the human society thrives. The weather and climate characteristics of any place on earth determine the types of crops that are grown for food. It is  said that of all the human activities, agriculture which provides food for people and contributes significantly to the economies of nations, is the most sensitive to weather. Normal weather conditions are associated with good crop yield and positive economic impact.

soil thermometer is of immerse importance to agriculture. Because there are some crops that are shallow rooted and others that are deep-rooted. It helps to know at what depth to plant the particular crop so as to have its maximum yield.

The thermometer gives various conditions at various depths which help to determine the temperature at which different crops can thrive.

Some crops need some kind of heat to thrive while some need cold conditions.